Throughout this application a power driven ski-bob (which will be called "Ski-bob") will be discussed with the understanding that what is said applies equally to power driven skis and other snow going vehicles, which in the claims will be referred to, commonly, as "a ski-bob type of a device".
A Ski-bob is a newcomer to the field of winter recreation. Presently there is a polarization between outdoor winter sports enthusiasts. The purists adhere to skis propelled by gravity or skier's muscles, while the modernists enjoy mounting a snowmobile which employs brute force to propel itself and its rider. Power driven ski devices (shown in my U.S. Pat. No. 3,853,192 and in the present application) bridge this gap between the purists and modernists. They do so by combining the excitement of using one's of balance to control and steer with the excitement of controlling one's propelling power, and they remove or reduce the objectionable aspects of snowmobiling. For example, the total weight of a current Ski-bob is around 30 pounds and it is propelled by a gas thrifty 3 HP engine, versus a typical snowmobile which weighs several hundred pounds and uses a gas guzzling engine ten times more powerful. Therefore, in contrast to snowmobiles, Ski-bobs have a minimal effect on the trail they pass, they do not develop large kinetic energy that may endanger their riders or others and they are not likely to get stuck in the snow, since the average rider can lift a unit in one hand. The small engine generates less acoustical energy which can be readily muffled to non-obtrusive levels.
One of the important parts of a Ski-bob is its propulsion system, and one of the propulsion system's key elements is the tread. Suitable treads are shown in the parent applications and in my copending application Ser. No. 831,163 filed on Apr. 25, 1977, which are herein incorporated by reference. As can be seen, these treads are designed to be very light, in order not to increase the weight of the Ski-bob, not to increase the power requirement and to minimize the inertial forces which are developed dynamically in the propulsion system. The snow engaging portions of the cleats are made of a resilient, usually plastic, material. The tread relies on snow for lubrication and cooling, but since the tread can run dry occasionally, for example during engine tune-up in a repair shop, etc., or almost dry as when running on icy surfaces, it is important to provide means for accommodating such situations without the tread wearing at an unacceptable rate.
Thus an important object of the present invention is to provide a means for reducing the tread's wear rate, especially when running dry.